When installing SxS assemblies in Vista, you may experience MSI error 1935, with HRESULT 0x80073715.
0x80073715 is Win32 error ERROR_SXS_MANIFEST_IDENTITY_SAME_BUT_CONTENTS_DIFFERENT.
// MessageId: ERROR_SXS_MANIFEST_IDENTITY_SAME_BUT_CONTENTS_DIFFERENT
// The identities of the manifests are identical but their contents are different.
#define ERROR_SXS_MANIFEST_IDENTITY_SAME_BUT_CONTENTS_DIFFERENT 14101L
This error means, you have tried to install two assemblies with the same identity but with different contents.
To workaround the issue, whenever you change the content of the assembly, you need to change the version number of the assembly.